The present invention relates to a control device for controlling a transmission device including an input member drivably coupled to an engine and a rotary electric machine capable of producing regenerative torque on the basis of a request to decelerate a vehicle, an output member drivably coupled to wheels, and a speed change mechanism that has a plurality of friction engagement elements that are controllably engaged and disengaged to switch between a plurality of shift speeds, and that outputs rotation of the input member to the output member while changing the rotational speed with a speed ratio of each shift speed.